This invention relates to waterproof electrochemical devices such as portable lighting devices, anti particularly to the type of such devices which have an electrochemical Cell that generates hydrogen gas.
Portable lighting devices such as lanterns and flashlights which employ batteries having aqueous electrolytes, e.g., alkaline MnO.sub.2 batteries, must provide means for safely eliminating the hydrogen gas which is evolved from the batteries as a result of corrosion reactions, charging, cell reversal, etc. This becomes an even more serious problem in sealed, waterproof lighting devices where the trapped hydrogen gas can explosively react with available oxygen in the air inside the housing when detonated by external static electricity or an internal spark generated, e.g., by the switch operation. This can happen, for example, in vented units when a person who has generated static electricity on his or her body reaches out to a lantern of this type.
Various venting means have been used in the prior art, e.g., as taught in U.S. Pat. No. 4,626,852 to Pennwalt Corporation. Applicant's U.S. Pat. No. 4,237,526 covers a waterproof lighting device having a gas vent opening covered with a hydrophobic membrane of microporosity sufficient to maintain the hydrogen concentration in the housing below 10 vol %. One-way vent valves have also been used (U.S. Pat. Nos. 5,207,502, 5,113,326 and 5,349,507).
Applicant's waterproof lanterns are currently made containing a small catalyst pellet (about 0.050 g) of palladium coated on an alumina (Al.sub.2 O.sub.3) substrate for catalytic recombination of evolved hydrogen with the oxygen present in the housing. However, this pellet does not always seem to be as efficient as needed to prevent hydrogen detonations, as discussed, for example, in U.S. Pat. No. 5,349,507.